The brittleness in thick section and the relatively poor stress crack resistance of parts molded from aromatic polycarbonate resins is a matter of common knowledge and experience. In addition, polycarbonates per se are difficult to melt process, e.g. to extrude and mold, because of their high melt viscosity. These problems have been partially overcome in the art by blending polyolefins or various rubbers into the aromatic polycarbonate resins. See, for example, Goldblum, U.S. Pat. No. 3,431,224, and German Pat. No. 2,329,585, dated Jan. 2, 1975, the disclosures of which are incorporated herein by reference. Unfortunately, these additives are somewhat limited in scope of use, because at high enough levels to cause significant advantageous effects, there is also a tendency to delaminate after molding, indicating a certain degree of incompatibility.
In applicants' copending application, U.S. Ser. No. 833,364, filed concurrently herewith, under Attorney's Docket GE-708 (8-CH-2705), and incorporated herein by reference, a major improvement is disclosed in providing high impact strength combinations of aromatic polycarbonate resins with remarkably enhanced flowability. The improvement comprises adding to the aromatic polycarbonate a selectively hydrogenated rubbery block copolymer.
It has now been discovered that aromatic carbonate resins per se can be even more remarkably improved in terms of impact strength, especially in thick walled moldings and processing improved if they are intimately admixed with a precompounded easily dispersible polymer system comprising the selectively hydrogenated rubbery block copolymer and a polyolefin resin, and, if desired, mixing in a further amount of a hydrogenated block copolymer.
The resulting compositions show no tendency to delaminate. They also have improved stress crack resistance; high aging resistance; and high heat resistance during processing.
It is believed that the surprising efficiency of the system is attributable to the special features of system (b). System (b) consists of (i) a precompounded mixture of a selectively hydrogenated vinyl aromatic-olefin-vinyl aromatic block copolymer and (ii) an olefinic resin, e.g., polyethylene, polypropylene, ethylene/propylene copolymers, and the like, at a ratio of 20/80 to 80/20, of (i) to (ii) by weight. In any case, dispersibility in component (b) can be further improved by adding an aromatic polycarbonate or polystyrene as a dispersing aid in an amount of up to 100 parts by weight of resinous components.
The new compositions may also be reinforced, e.g., with fibrous glass, and rendered flame retardant with flame retardant additives to extend their field of use in molded products.